The present invention is directed to controlled release compositions. More particularly, the invention is directed to an expanded, porous, cellulosic carrier material impregnated with an additive material for subsequent release or chemical reaction, and to its process of manufacture. According to the present invention, cellulosic pulp rejects from a papermill are partially dewatered; flash-dried to cause the rejects to expand and become porous; an additive material to be slowly released is applied to the expanded porous cellulosic rejects, and then dried. The cellulosic carrier material holds or retains the additive for delayed release.
It is recognized that there are numerous compositions which are necessarily or most advantageously applied for slow release over a period of time. Such compositions include fertilizers, plant growth stimulants, herbicides, pesticides, and fungicides. As a result of this need, various time or controlled release compositions have been proposed. U.S. Pat. No. 4,388,352 discloses a time-released composition wherein a carrier such as never-dried cellulosic pulp is immersed in a solution of an impregnant, such as a solution of fertilizer; the mixture distilled to exchange the fluid in the pores of the carrier with the solution of the impregnant, and thereafter the carrier is dried to entrap the impregnant within the pores. According to the patent disclosure, during the distillation process the solution of impregnant diffuses through the pulp to displace the water otherwise in the pores. The pulp is then dried. During the drying, the pores of the never-dried pulp irreversibly collapse. The collapse of the pores is the manner in which the impregnant is trapped within the pulp. Accordingly, the carrier material in the final composition is not porous and, therefore, the additive material must pass through the carrier material for release.
U.S. Pat. No. 3,172,752 discloses a controlled release substance having an active material such as a herbicide, fungicide or insecticide suspended in or on perlite as a carrier material which is then coated. In the processing the carrier material is preheated to remove some of the water contained therein. Thereafter, the perlite is heated by means of a hot gas and caused to expand. The expanded perlite particles, according to the patent, provide a relatively inert particulate base for an active material. A holding material is added to the composition so that the additive material will more readily adhere to the perlite base. The holding material can be a material such as lignite, sea kelp, activated sewage sludge, or sulfide paper pulp liquor. Perlite, being a hard glasslike material, has limitations both from the standpoint of its treatment and from its end uses.
U.S. Pat. No. 3,269,824 discloses a wastepaper soil conditioning and fertilizing pellet. According to the patent, wastepaper is repulped and water is then added to it, and the mixture cooked under pressure into a slurry of finely divided cellulose fibers. Fertilizers and other elements are then added to the slurry and thoroughly mixed. The resultant composition is drained into a vacuum chamber where excess moisture is drawn off until the slurry reaches the consistency of a stiff dough. The slurry is then packed into a metal cylinder and extruded into strands which are then cut into pellets. Any moisture remaining in the pellets is removed by drying under infrared lamps as the pellets move from the extrusion step along a conveyor belt. Upon application to soil, the moisture in the soil causes the densified pellets to expand gradually to double or triple their compressed volume while drying of the soil will cause the pellets to contract. The method of manufacture is time-consuming and expensive.
Although the aforesaid methods and compositions are useful and each has certain advantages, none is completely acceptable from the standpoint of cost of materials and processing, stability and structural integrity of the composition, versatility of the carrier material so as to permit the use of a single carrier material for a plurality of additive materials, or availability of the carrier materials in diverse locations so as to permit manufacture of the compositions at or close to the point of use.